AbstractThe antifungal activity of the lactoperoxidase (LPO) system with glucose oxidase (GOD) as source of hydrogen peroxide was determined in salt solution and in apple juice. The test organismsRhodutorula rubraandSaccharomyces cerevisiaewere cultivated aerobically in apple juice,Mucor rouxiiwas grown on wort agar adjusted to pH 4.5.Aspergillus nigerandByssochlamys fulvawere kept on malt extract agar. Spores of the filamentous fungi were harvested by suspension in salt solution supplemented with Tween 80® and checked microscopically. The antifungal activity of the combined enzyme system was tested with initial counts of approx. 105cfu · ml−1(yeast cells or spores) suspended in salt solution supplemented with 25 mg · l−1thiocyanate and 20 g · l−1glucose or in apple juice supplemented with the same amount of thiocyanate. The tests were performed with 25 ml of the medium in 100 ml Erlenmeyer flasks shaken at 28 °C under aerobic conditions. Inactivation was achieved for all test organisms in both media. The yeast strains were found to be least stable whileB. fulvawas most resistant. A combination of 5 U · ml−1LPO with 0.5 to 1 U · ml−1GOD was sufficient for complete inactivation of this mold in salt solution within 2 h. The enzyme system also showed antifungal activity in apple juice at acid pH (3.2), although its effectiveness was reduced. In this medium,B. fulvawas inactivated by 20 U · ml−1LPD and 1 U · ml−1GOD within 4 h.R. rubraandS. cerevisiaewere unable to survive in apple juice at 5 U · ml−1LPO combined with 1 U · ml−1GOD. For inhibition by GOD alone, higher amounts of this enzyme were needed and even then onlyM. rouxiiandR. rubrahave been affected within the concentration range